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Contagious Equine Metritis

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Contagious equine metritis (CEM) is a venereal disease of horses caused by the

bacteria Taylorella equigenitalis. It can impact fertility in both mares and stallions.

The United States is considered to be CEM-free. Therefore, CEM is a foreign animal

disease that is reportable at both the Federal and State level. The U.S. horse

industry could suffer significant economic losses if the disease became established

here.
CEM is spread during breeding or through contact with contaminated objects. It is

highly contagious among horses and can be difficult to detect and control. Signs of

illness in infected mares may not be obvious, and stallions carry the bacteria without

showing any signs at all. In some cases, mares may also become carriers. Foals born

to infected/carrier mares can also become long-term carriers of the bacteria.

What To Look For

Stallions show no signs of infection and become disease carriers. Mares typically

clear infection without treatment but can also become carriers.

In mares, symptoms usually appear 10–14 days after infection and include:

Vaginal discharge (in up to 40 percent of affected mares)

Infertility

Abortion

How To Prevent This Disease

CEM can be transmitted by an infected horse during breeding; through artificial

insemination with contaminated semen; or by contact with contaminated objects,

such as hands or instruments. It can also be spread during the semen collection

process. There is no vaccine.

Import Restrictions for Horses

To keep this disease out of the United States, USDA requires stallions and mares

imported from CEM-affected countries to quarantine and test negative for CEM

before they can enter the country. Learn more about U.S. import restrictions for

horses.

Biosecurity Precautions During Breeding

As a horse owner or breeder, here's what you can do to prevent the spread of CEM:

Test stallions annually for T. equigenitalis before each breeding season.
Maintain accurate and up-to-date breeding records, including breeding date

and stallion used, to quickly identify infection source and limit disease spread.

If your mares are having reproductive problems or have symptoms of

contagious equine metritis, contact your veterinarian.

Always clean and disinfect semen collection equipment between stallions.

How It Is Treated

Animal health officials investigate each detection to identify, test, and treat all

infected or exposed horses. Affected horses are quarantined and treated with

antimicrobials to eliminate T. equigenitalis. They are retested and not cleared for

release from quarantine until results are negative. After treatment, fertility appears

to return to normal in recovered horses.

Treatment is performed in quarantine under the supervision of regulatory animal

health officials. Personnel thoroughly wash the external genitalia in stallions and

mares using a disinfectant soap (for example, 2% Chlorhexidine). After thoroughly

rinsing the area, they apply a topical antibiotic (for example, nitrofurazone or silver

sulfadiazine). Steps need to be repeated for 5 consecutive days. Most horses

respond very well to one 5-day treatment; however, some may need to be retreated.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their

veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health,

zoo, or wildlife personnel; and others) report diagnosed or suspected cases of

nationally listed reportable animal diseases to APHIS District Offices and to the State

animal health official as applicable under State reporting regulations. 

Controlling Contagious Equine Metritis

Confirmed CEM Cases in the United States
CEM has been detected sporadically in the United States, most recently in 2013.

USDA oversees quarantine, testing, and treatment programs for CEM. We have

eradicated the disease from the U.S. equine population after each detection.

May 2013

In May 2013, USDA's National Veterinary Services Laboratories (NVSL) confirmed

that a Thoroughbred mare in Puerto Rico was positive for Tayorella equigenitalis, the

bacterium that causes CEM. NVSL determined that the T. equigenitalis isolate from

this mare matched a strain detected previously in Europe and the United States,

most recently in an Arabian stallion in Arizona in 2011.

The positive mare was born in the continental United States in 2011. She was moved

to Puerto Rico just before she was confirmed to have CEM based on three positive

complement fixation tests and a positive culture at NVSL. She subsequently

completed a course of antibiotic treatments for T. equigenitalis and was re-tested

with negative results.

A thorough epidemiologic and diagnostic investigation of this case was conducted.

Potentially exposed horses were investigated and tested in Puerto Rico and three

States. No additional positive horses were detected and no relationship was found

between the positive mare and any horses associated with previous U.S. cases of

CEM.

February 2013

In February 2013, NVSL confirmed that a Lusitano mare in south-central California

was positive for T. equigenitalis, the bacterium that causes CEM. NVSL determined

that the strain of the bacterium did not match any T. equigenitalis strains ever found

in the United States, indicating this case was not related to any previous U.S. cases

of CEM.

In addition to the positive Lusitano mare, two exposed stallions and one exposed

mare were subsequently found positive for T. equigenitalis. All four positive horses

were treated, re-tested with negative results, treated again, and released from

quarantine. Additionally, a filly foal born to one of the positive mares in 2013 was

tested with negative results, treated, and released from quarantine along with her

dam.
A thorough epidemiologic and diagnostic investigation was completed. The positive

Lusitano mare was imported as a foal from a country not known to be affected by

CEM. She was bred to a Lusitano stallion in California. That stallion was imported as

an adult from the same country as the positive mare, and he was one of the two

exposed stallions found positive with a strain of T. equigenitalis that matched the

strain from the positive mare. The second positive stallion was a domestic Lipizzan

that had semen collected at the same facility as the positive Lusitano stallion in

2012. The second positive mare was a domestic cross-bred Andalusian. She had

been bred by artificial insemination to the positive Lusitano and became pregnant.

The imported Lusitano stallion was determined to be the source of infection for the

other three horses. Culture of frozen semen indicates the stallion had been infected

since at least 2009 and likely was carrying the infection at importation.

Along with the positive horses, a total of 18 exposed horses were identified and

quarantined, including the foal of the positive mare. Eleven exposed stallions in

California, including a gelding exposed as a stallion, and one exposed stallion in

another State, were tested with negative results, treated, and released from

quarantine. There were also five exposed mares in quarantine for testing and

treatment in California and two other States. Each exposed horse identified in the

investigation completed a testing and treatment protocol to determine its CEM

status.

July 2011

In July 2011, NVSL confirmed that an Arabian stallion on a central Arizona premises

was positive for T. equigenitalis, the bacterium that causes CEM. NVSL also

determined that the strain of the bacterium did not match any T. equigenitalis

strains previously found in the United States, indicating this case was not related to

the California CEM case in May 2010, the multi-State CEM outbreak in late 2008, or

imported stallions found positive in 2006.

The positive stallion was born in Arizona in 2007. He was tested for CEM to meet

requirements for international shipment of his semen. After testing positive, the

stallion received antibiotic treatment for T. equigenitalis and was re-tested with

negative results.

A thorough epidemiologic and diagnostic investigation of the case was conducted.

Information from the investigation indicates that 17 other stallions in 2 States, and
13 mares in 6 States, were exposed to the positive stallion. Although one exposed

mare died of unrelated causes before completing testing, all other exposed stallions

and mares completed a testing protocol to determine their CEM status. All 29 of

those exposed horses (17 stallions, 12 mares) were found negative for T.

equigenitalis.

May 2010

In May 2010, NVSL confirmed that an Arabian stallion on a southern California

premises was positive for T. equigenitalis, the bacterium that causes CEM. A

thorough epidemiologic and diagnostic investigation was carried out to determine

the origin of the CEM bacterium. Final analysis of the epidemiologic and diagnostic

findings from the investigation indicated that the positive Arabian stallion was

contaminated with T. equigenitalis prior to his arrival in the United States and that

no further spread of the bacterium occurred after he arrived. The positive imported

stallion successfully completed antibiotic treatment and was confirmed to be free of

T. equigenitalis.

The positive stallion was imported into the United States in March 2010 from a

country not known to be affected by CEM. NVSL determined that the strain of the

isolated bacterium did not match any T. equigenitalis strains previously found in the

United States, indicating this case was not related to the multi-State CEM outbreak

in late 2008.

A total of 23 horses exposed to the positive imported stallion were located and

tested for T. equigenitalis. Five exposed stallions were located in California, and 18

exposed mares were located in a total of 8 States. All exposed horses completed an

appropriate testing protocol and were found negative for T. equigenitalis.

December 2008

In December 2008, a Quarter Horse stallion on a central Kentucky premises was

confirmed by NVSL as positive for T. equigenitalis, the bacterium that causes CEM. A

thorough epidemiologic and diagnostic investigation was carried out to determine

the origin of the CEM bacterium. Final analysis of epidemiologic and diagnostic

findings from the investigation indicated that a stallion imported from Denmark in

late 2000 was the likely source of the outbreak. The source stallion and 27 other

horses found positive in the outbreak were treated with antibiotics and confirmed
free of T. equigenitalis.

NVSL determined that the strain of T. equigenitalis found in this outbreak did not

match any strains found in other U.S. outbreaks or cases of CEM, indicating that this

outbreak was not associated with cases found in three imported stallions in 2006.

Further investigation and testing of exposed horses found a total of 5 mares and 23

stallions, including one that is now a gelding, positive for T. equigenitalis. The 23

positive stallions were found in 7 States: 1 in Georgia, 3 in Illinois, 3 in Indiana, 1 in

Iowa, 4 in Kentucky, 1 in Texas, and 10 in Wisconsin. The five positive mares were

found in three States: two in California, two in Illinois, and one in Wisconsin.

In addition to the 28 positive horses, another 977 horses were exposed to T.

equigenitalis in the outbreak. The 1,005 horses were found in 48 States. A total of

278 exposed or positive stallions were found in 31 States, and 727 exposed or

positive mares were found in 46 States. Hawaii and Rhode Island were the only

States in which an exposed or positive horse was not found.

Overall, 971 (96.6 percent) of the 1,005 horses were found to be free of T.

equigenitalis. Six of the eight States that had a positive horse (California, Georgia,

Indiana, Iowa, Kentucky, and Texas) completed the testing and treatment of all

known positive and exposed horses. The remaining two States with positive

horses—Illinois and Wisconsin—completed treatment and negative re-testing of all

positive horses, but one or more exposed horses remained under quarantine in each

of those States because they completed only one set of negative cultures.

Of the 278 stallions, 261 (93.9 percent) completed an appropriate testing and

treatment protocol and were found negative for T. equigenitalis. Another 14 exposed

stallions (5.0 percent) had one set of negative cultures but remained under

quarantine indefinitely unless testing and treatment were completed in full. Three

exposed stallions (1.1 percent) died, one after testing negative on one set of

cultures and two prior to any testing.

Of the 727 mares, 710 (97.7 percent) completed testing and treatment and were

negative for T. equigenitalis. Eight exposed mares (1.1 percent) did not complete

their testing and remained under quarantine indefinitely unless testing and

treatment were completed in full. The remaining nine mares (1.2 percent) were not

tested, either because it was determined that they were never actually exposed or

because of the mare's death prior to testing.
The investigation of this outbreak determined that all four of the positive Kentucky

stallions were on the central Kentucky premises during the 2008 breeding season.

The Texas and Indiana stallions also spent time on the Kentucky premises during

2008. The positive Wisconsin stallions were not in Kentucky, but four of them were

co-located during at least one breeding season in Wisconsin with a positive stallion

that was on the Kentucky premises in 2008. The fifth, sixth, seventh, eighth, ninth,

and tenth Wisconsin stallions all spent time at a breeding facility used by the fourth

positive Wisconsin stallion, by the three positive Illinois stallions, and by the Iowa

stallion (now a gelding). The positive Georgia stallion was co-located with three

positive Wisconsin stallions in 2008.

The positive Wisconsin mare was bred by the second positive stallion in Wisconsin.

Each of the positive mares in Illinois and in California was bred by artificial

insemination (AI) in 2008 using semen from a positive stallion. Both California mares

were exposed by AI to the first positive stallion in Wisconsin, and the first Illinois

mare was exposed to a positive stallion now in Indiana. The second positive mare in

Illinois was exposed by AI in 2008 to the second positive Illinois stallion.

Distribution

The first cases of CEM were diagnosed in the 1970s, beginning in England and then

in other countries in Europe and the United States. Due to the nature of CEM, it is

difficult to determine how widely it is distributed throughout the world. USDA

considers Japan, South Africa, Korea, all European Union countries, and many other

countries in Europe (including Great Britain and Northern Ireland) to be affected with

the disease. Visit the World Organisation for Animal Health for the latest information

on CEM reporting around the world.

Testing

Veterinarians work with State or Federal animal health officials to test any horse

suspected of having CEM or any horse exposed to a CEM-positive animal. You may

also need to test for CEM to meet requirements for exporting horses, semen, or

embryos to another country or as part of a routine breeding soundness examination.

There are three ways to test for CEM: bacterial culture, blood testing, and test

breeding.
Bacterial culture tests look for the bacteria that cause CEM. Veterinarians collect

swabs and send them to approved laboratories. They require special handling and

must be processed within 48 hours of collection. It takes 7 days to get a result.

Typically, the veterinarians will collect three sets of swabs for culturing during a 7- to

12-day period.

Blood testing looks for an immune response to CEM, which helps determine if a

horse has recently been exposed to the disease. This complement fixation test can

only be used in mares because stallions do not develop an immune response to

CEM.

Test breeding is used to detect CEM in stallions under certain circumstances. A

stallion is bred to two mares known to be CEM-free. Those mares are then tested for

CEM. It takes 5 weeks after the test breeding and multiple tests on the mares to

declare the stallion negative. Test breeding will sometimes detect bacteria that

direct testing of the stallion did not detect. To maximize the chances of detecting

the bacteria, USDA requires stallions to be tested by both bacterial culture and test

breeding if they are known to have been exposed to the CEM bacteria or are being

imported to the United States from a CEM-affected country. Test breeding is not

normally required to export stallions or semen to another country. Mares are tested

with bacterial culture and blood tests.

Recommended Sources for More Information

Contagious Equine Metritis (430.44 KB) (APHIS factsheet)

WOAH: Contagious Equine Metritis (World Organisation for Animal Health)